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A few tens of milligrams of dissolved metal per litre is enough to wreck a formulation. It yellows a shampoo, catalyses the decomposition of a peroxide bleach, scales a cooling circuit, or turns a clear liquid detergent hazy on the warehouse shelf. The fix is a chelating agent — a category, not a product, and the six workhorses in it are not interchangeable. The choice comes down to three questions: which metal you need to bind, at which pH the system runs, and what the destination market permits.
Ethylenediaminetetraacetic acid, CAS 60-00-4, C10H16N2O8, molecular weight 292.24, is the parent of the whole family: a white crystalline powder at 99% minimum purity, melting point 240 °C with decomposition. Its specification carries an uncomfortable line — solubility: slightly soluble in water — with a 1% solution sitting at pH 2.5 to 3.5. The acid is only sparingly soluble because it is four carboxylic acids waiting to be neutralised. In practice most users dissolve it by dosing sodium hydroxide or sodium carbonate in the vessel, converting it in situ to the soluble sodium salt. Where the process has a neutralisation step anyway, the acid is the economical form: on a molar basis, a kilo of the acid carries more chelant than a kilo of any of its salts. Where it does not, buying the salt is cheaper than building the step.
Tetrasodium EDTA, CAS 64-02-8, C10H12N2Na4O8, molecular weight 380.17, is what the acid becomes after full neutralisation — a white crystalline powder melting above 300 °C that goes into water at 0.1 g/mL to a clear, colourless solution. This is the form with the widest spread of uses: a water softener in fibre refining, bleaching and dyeing, where it ties up the calcium and magnesium that would otherwise deposit on the goods; a component of the initiator system in styrene-butadiene rubber polymerisation, where it holds iron out of the reaction; and the standard chelant in liquid detergents and cosmetic formulations, where a fraction of a percent keeps the product clear through its shelf life. The trade-off against the acid is arithmetic: the four sodium atoms ride along at no benefit, so per kilogram of powder there is less active chelant. The benefit is process simplicity.
Ordinary EDTA cannot tell useful calcium from troublesome trace metals; it binds whatever is available. In a food or pharmaceutical system that is a problem, because the formulation may rely on its calcium. Calcium disodium EDTA, CAS 23411-34-9, molecular weight 374.27, solves this by arriving pre-chelated: the calcium is already inside the molecule, pH 6.5 to 8.0 in solution, freely soluble, 99% minimum purity. A pre-chelated calcium centre is not easily displaced, so the salt removes unwanted iron and copper without pulling calcium out of the product. That is why it, not plain EDTA, is the form used in food-related formulations, personal care and pharmaceuticals where system stability governs. It is packed in 25 kg bags with 5 kg small packs available, 24 month shelf life.
Flip the purpose and the same chemistry works in reverse. Ferric sodium EDTA, CAS 15708-41-5, C10H12FeN2NaO8, is EDTA holding an iron atom — 12.5% ± 0.5% iron content, a yellow to yellow-brown powder, pH 4.0 to 6.0 in a 1% solution, completely water soluble. The chelated iron resists oxidation and precipitation, so it stays in solution and absorbable where ordinary iron salts would have become rust-brown hydroxide long before reaching their target. In food fortification it is the iron source used in soy sauce, cereal products and condiments, with absorption better than ferrous sulfate at lower organoleptic impact. In agriculture it is the chelated iron in water-soluble and foliar fertilisers, correcting chlorosis and — a point that decides whole product lines — remaining stable in neutral and slightly alkaline soils where ferrous sulfate locks up within weeks. Feed, food and agriculture grades differ mainly in documentation, so state the grade on the enquiry.
EDTA wraps a metal with six donor sites. Pentasodium DTPA, CAS 140-01-2, molecular weight 503.27, a white to off-white powder at 99% minimum purity, offers eight — three amine nitrogens and five carboxyl oxygens — and the stability constants show it, particularly against ferric iron. Two consequences matter commercially. First, it keeps working over a wider pH range and in strongly alkaline systems where EDTA loses grip, which is why it stabilises hydrogen peroxide in paper bleaching: peroxide plants live at pH 10 and above, and any iron that slips through catalyses the peroxide into nothing. Second, its affinity list — calcium, magnesium, iron, copper — covers the scaling ions in circulating cooling water, boiler water and membrane systems, where it keeps heat-transfer surfaces clean. It comes as the pentasodium salt because the parent acid is not conveniently soluble. 25 kg bags, 500 kg jumbo bags, 24 month shelf life.
EDTA has one weakness that has nothing to do with performance: persistence. It is poorly biodegradable, routinely detected in surface waters, and ecolabel schemes in Europe restrict it in consumer detergents. Sodium glucoheptonate, CAS 31138-65-5, molecular weight 264.16, is the substitution candidate that actually works: a white to off-white powder, freely soluble, pH 6.5 to 8.5 in a 10% solution, good biodegradability, low toxicity. It chelates calcium, magnesium and iron credibly, which carries it through industrial cleaners, cooling-water scale control and metal surface treatment. It has a second life in construction, where it serves as a retarding and dispersing agent in concrete admixtures. Where a customer's brief says "no EDTA", this is usually the first molecule to test. Citric acid monohydrate, CAS 5949-29-1 remains the fully food-grade baseline: pH 2.2 to 2.5 in a 1% solution, 1630 g/L water solubility, modest chelating power but an unanswerable safety file.
In micronutrient work the chelant is chosen to match the metal salt it must carry: NaFeEDTA for iron in alkaline soils, with zinc acetate dihydrate and magnesium sulfate as the conventional zinc and magnesium sources where chelated grades are not justified by the crop economics. In cleaning formulations the chelant works alongside the alkalinity — sodium carbonate builders the wash liquor while the chelant handles the polyvalent ions the carbonate would otherwise precipitate as scale.
Four lines make a chelant quotation comparable: the metal ion to be controlled and roughly how much of it; the operating pH of the system, since this alone eliminates half the catalogue; the destination market and grade — food, feed, agriculture or industrial — because documentation, not chemistry, separates the grades; and the form wanted, acid or salt. Packaging across the family is uniform — 25 kg bags, jumbo bags on the bulk end — with 24 month shelf life in cool, dry storage. Ask for TDS, COA and SDS with the sample, and check which ecolabel schemes the material is cleared for before the formulation is frozen around it.
